In the field of microfabrication represented by fabrication of integrated circuit devices, a lithographic technology enabling microfabrication with a line width of 0.20 μm or less has been demanded in order to achieve higher integration.
A conventional lithographic process utilizes near ultraviolet rays such as i-line radiation. It is known in the art that microfabrication with a line width of a sub-quarter micron order using near ultraviolet rays is very difficult.
Therefore, use of radiation with a shorter wavelength has been studied for enabling microfabrication with a line width of 0.20 μm or less. As radiation with a shorter wavelength, deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, a KrF excimer laser (wavelength: 248 nm), an ArF excimer laser (wavelength: 193 nm), an F2 excimer laser (wavelength: 157 nm), EUV (wavelength 13 nm), and electron beams have attracted attention.
As a radiation sensitive resin composition applicable to the short wavelength radiations, a number of compositions utilizing a chemical amplification effect between a component having an acid-dissociable functional group and a photoacid generator which generates an acid upon irradiation (hereinafter called “exposure”) has been proposed. Such a composition is hereinafter called a chemically-amplified radiation sensitive composition.
As the chemically-amplified radiation sensitive composition, Japanese Patent Publication No. 27660/1990 discloses a composition comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the polymer to release a t-butyl ester group or t-butyl carbonate group by the action of an acid generated upon exposure to form an acidic group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist film readily soluble in an alkaline developer.
As characteristics demanded of a photoacid generator for a chemically-amplified radiation sensitive composition, superior transparency to radioactive rays, high quantum yield in acid generation, and capability of producing an acid exhibiting high acidity, high boiling point, and a suitable diffusion distance (hereinafter referred as diffusion length) in the resist film can be given.
To ensure high acidity, high boiling point, and appropriate diffusion length, the structure of an anionic moiety in the ionic photoacid generator and the structure of a sulfonyl moiety in the nonionic photoacid generator comprising a sulfonyl structure or a sulfonic acid ester structure are important. When the photoacid generator possesses a trifluoromethanesulfonyl structure, for example, even though a sufficiently strong acid to ensure adequate resolution performance of a photoresist is generated, there is a drawback of a high mask dependency due to the low boiling point and long diffusion length of the generated acid. When the photoacid generator possesses a sulfonyl structure with a large organic group such as a 10-camphorsulfonyl structure, even though the mask dependency is low due to the high boiling point and short diffusion length of the generated acid, the resolution performance as a photoresist is insufficient due to the poor acidity.
On the other hand, photoacid generators having a higher perfluoroalkylsulfonyl structure such as perfluoro-n-octane sulfonic acid (PFOS) have been given attention in recent years due to the adequate acidity, boiling point, and diffusion length.
However, the photoacid generators possessing a higher perfluoroalkylsulfonyl structure such as PFOS have environmental problems of low combustibility and accumulation in the human body. A regulation on their use has been proposed by the U.S. Environmental Protection Agency (see “Perfluorooctyl Sulfonates; Proposed Significant New Use Rule”).
If a chemically amplified resist exhibiting poor film surface smoothness is used in devices with a design width on the order of a subhalf micron or less requiring a more precise line width control, irregularities (such as nano edge roughness) on the film surface is transferred to a substrate when a resist pattern is transferred to the substrate by an etching process or the like, giving rise to a decrease in pattern dimensional accuracy and impaired electric performance in the obtained devices (see, for example, J. Photopolym. Sci. Tech. p. 571-576 (1998); Proc. SPIE Vol. 3333, p 313-323(1998); Proc. SPIE Vol. 3333, p 634-642 (1998); and J. Vac. Sci. Technol. B16(1), p 69-76 (1998)). Therefore, in addition to exhibiting excellent resolution performance, chemically amplified radiation sensitive resin compositions are required to provide excellent surface smoothness after formation of the resist pattern.
For these reasons, there is an urgent need in the field of microfabrication for the development of an alternative component which can produce a chemically amplified radiation sensitive resin composition having no defects originating from the higher perfluoroalkane sulfonyl structure, excelling in resolution performance, and causing only slight nano edge roughness, and which also excels as a photoacid generator.
The object of the present invention is to provide a novel photoacid generator which exhibits high transparency to ultraviolet rays such as a KrF excimer laser, ArF excimer laser, F2 excimer laser, or EUV, and electron beams, exhibits comparatively high combustibility and no bioaccumulation, produces an acid exhibiting high acidity, high boiling point, moderately short diffusion length in the resist film, and low dependency on the mask pattern density, and produces a resist pattern excelling in surface and sidewall smoothness; a sulfonic acid generated from the photoacid generator; a sulfonyl halide compound useful as a raw material or intermediate for synthesizing the photoacid generator; and a positive-tone or negative-tone radiation sensitive resin composition containing the photoacid generator.